Iron(II) Bis(acetylide) Complexes as Key Intermediates in the Catalytic Hydrofunctionalization of Terminal Alkynes

Nonclassical
iron­(II) polyhydride complexes supported by PNP-pincer
ligands were found to be very active catalysts for the Z-selective hydroboration and head-to-head dimerization of terminal
alkynes. Iron­(II) bis­(acetylide) complexes are identified as catalytically
active species in both transformations, which proceed via different
reaction pathways, however. These species as well as intermediates
relevant for the elucidation of selectivity could be trapped and fully
characterized spectroscopically. X-ray structures of key intermediates
are presented. Detailed DFT calculations provide a deeper insight
into the activation of the precatalysts, and comprehensive catalytic
cycles are elucidated. The proposed mechanisms provide a consistent
picture of the different reaction pathways and fully explain the stereoselective
steps of these transformations.